Why do we watch movies? No, really, why is it? As close an answer as we’ve ever come to for our own, fairly evident obsession with what we consider the greatest storytelling medium humankind has ever developed, is well, that life is short. Bear with us a second on this: basically to submerge yourself in a story well-told is a way to live out other lives within your own, and through those complex and magical processes of identification, to breathe and dream and feel things that your own short span might otherwise never afford you. Of course for many movies, that experience, of killing a mutant robot or whatever, may have evaporated before you’ve picked the last of the popcorn husks from between your teeth. But occasionally, very rarely, we experience the cinema not of escape but of exploration in which the discoveries you make stay with you and become knitted into the fabric of your memory as surely as if you’d really been there, really done that. And so it was with Abdellatif Kechiche’s “Blue is the Warmest Color,” one of our most transportative, truthful and sublime movie experiences at Cannes this year. The wags among us might suggest that the 3-hour film overwhelmed us with its sheer length but truth be told we could have watched, or rather lived Adèle, as brought vividly and unforgettably to life by Adèle Exarchopolous (Cannes Best Actress, along with Lea Seydoux) for hours more.

Loosely based on a graphic novel, the film spans a brief but tumultuous period in Adèle’s life, from her last years of high school till some time later, when she is a twentysomething adult pursuing a career as a teacher. But it’s really about a defining relationship, told from the point of view of one of its participants. This is the story of Adele’s first love, the pain and the magnificence of all the insecurity, joy and self-discovery that goes along with that, right up to the relationship’s end and beyond. It’s the kind of insightfulness that finds its nearest recent equivalent for us in Derek Cianfrance’s “Blue Valentine” but ‘Warmest Color’ goes much, much further. And yes, the central relationship is between two women — we’re resisting the handy “lesbian movie” tag up front because, while we can’t push water uphill, neither do we want to contribute to the reductive categorisation of a film that deserves as wide an audience as possible. It’s a film about lesbians, but it’s for anyone with a brain and heartbeat and a halfway functional empathy gene.

Adèle is a bright, articulate high school student who reads voraciously and whose favorite subject is French literature. She is (hetero)sexually active, if not as provocative and crude about it as some of her schoolmates, and has a crush on a boy in the year above, with whom she goes out on a few dates. But on her way to meet him one day, she makes momentary eye contact with a girl with blue hair, Emma (Seydoux), an art student and an “out” lesbian a few years older than her, and finds she cannot forget her. They meet again, and over time their relationship becomes physical, they fall deeper in love and eventually move in together when Adèle leaves school. Differing outlooks on creativity and career paths and different social backgrounds (their parents are contrasted in dinner scenes that have a light brush of social satire to them) put strains on their relationship, but their love is a strong, passionate and mutually fulfilling bond for the most part, until complacency sets in and Adèle commits a breach of trust which Emma cannot forgive.

One of the refreshing aspects here is that although the sexual orientation of the central pair is never shied away from (certainly not in the detailed, graphic sex scenes), the film largely eschews the traditional LGBT coming out narrative, and aside from an ugly scene in the school grounds early on, that aspect of Adèle’s development is largely backgrounded until later in the film. Much more central to that relationship are trust and compatibility questions that are utterly relatable no matter what your sexuality. The film steadily and steadfastly refuses to define Adèle by her sexual orientation, preferring instead to build a nuanced and detailed portrait of who she is as a person.

It helps that the performances are this good. Seydoux is a revelation — it’s the first time we’ve seen her play the more mature, experienced partner as opposed to the ingenue, and her Emma is a wonderful creation, utterly believable in her free-spirited kindness, and truly luminous in her love for Adèle. But Exarchopoulos is the one who’s onscreen every moment, often in unflinching closeup, (she was chosen by Kechiche after an extensive search) and there is not a single one of those moments in which we felt her “acting.” The process by which she ages, or rather gains in maturity and loses the puppyish innocence of her teenage years is simple, subtle and completely believable, and her evocation of the agonies and ecstasies of love, and the gentle sadness of losing a little of one’s naivete in the inevitable process of growing up, pretty much erases the barrier, not just between actress and character, but between audience and character, too.

Our only niggle is actually with what will probably prove the film’s most chatter-worthy element: the sex scenes. In fact, there’s really just the one that bothered us, but not for the laudably explicit, often beautiful and unmistakably graphic nature of its portrayal of passionate, life-changing lesbian sex — just for its length. We hope it’s not prudishness, but somewhat taking the Soderbergh stance that “as soon as someone gets naked, the film becomes a documentary,” that scene’s overlength did in fact take us out of the story: by a certain point we had understood the drama and import of this moment for Adèle, and her revelatory experience of having sex, for the first time, with someone she was terrifyingly in love with. But as it ran on and on we found ourselves escaping the film’s spell a bit and starting to contemplate the spectacle of the flesh in itself, or the fact that hey, wow, Léa Seydoux is totally doing that! It’s the only time we felt anything as artificial as a cinematic point being made, and it’s a tiny fly in the ointment. Similarly an early scene in which Adèle fantasizes about the blue-haired girl while masturbating is a little anomalous to the rest of the film, again, not thematically, but stylistically as we see what she’s thinking in a way we never do again.

We can’t stress how minor those quibbles are compared with the overall scale of Kechiche’s achievement, though. This is absolute cinema, absolute characterization, absolute storytelling, controlled and compassionate, and bursting with empathy and life. Its theater-unfriendly length, along with the relative obscurity of the director, its language, explicit sex scenes and unavoidable “lesbian” descriptor mean this is unlikely to get the exposure some of our other festival favorites are guaranteed. But while it’s great to get ahead of the curve on those other movies, this is really the kind of film we come to Cannes in hopes of discovering. In fact, an experience this satisfying, moving, enriching and immersive might well have been worth the plane fare alone. “Blue is the Warmest Color” is a masterpiece of human warmth, empathy and generosity, because in a mere three hours, it gives you a whole new life to have lived. [A]